The present invention relates to a device for use in retrieving geotechnical and environmental soil samples, and in particular, to a split barrel core sampler having a locking configuration to prevent movement of corresponding barrel halves in a direction perpendicular to a plane that divides the barrel into two halves.
Earth probing for environmental and geotechnical soil sampling has become increasingly necessary. Sampling may be done by drilling into the earth and taking samples at predetermined depths, or by driving samplers into the earth. Where possible, driving samplers is usually less expensive and more convenient than drilling. Samplers may be advanced into the earth by pounding, vibrating, and/or pushing the upper end of a drill string to which the sampler is attached.
Samplers used to obtain geotechnical and environmental soil samplers typically use a split barrel design. A complete split barrel sampler assembly consists of a drive shoe for driving into the soil, a two piece split barrel, and an adapter coupling. The split barrel is a tubular member, typically having a round cross-section, split lengthwise to facilitate removal of soil samples contained therein after it is driven in the earth. Typically both ends of the split barrel are externally threaded, and the drive shoe contains a tapered tip on one end for cutting through soil, and an internal thread on the opposite end for mating with the split barrel. Typically the split barrel is attached to a drill rod with an adapter coupling that has internal threads on one end for mating with the drill rod and internal threads on the opposite end for mating with the split barrel.
The sampler is typically driven into the earth a distance approximately equal to the length of the split barrel. The sampler is then pulled from the earth by removing the entire drill string. The drive coupling and drive shoe are removed from the split barrel and the barrel halves are opened up to expose the sample soil. It is very time-consuming to add drill rod for lowering the sampler to the sampling depth, and likewise, to remove drill rod for raising the sampler from the sampling depth. Therefore, it is desirable to use as long of a split barrel as possible to minimize rod handling.
When the drive shoe and the adapter coupling are threaded onto the ends of the split barrel, they constrain the barrel halves from moving with respect to each other in all directions. However, at the middle of the split barrel, there is little influence from the end constraints, especially for longer end barrels. Typical existing split barrel designs utilize a tongue and groove feature that interlocks to prevent lateral movement of one barrel half relative to one another with respect to an axis. However, the tongue and groove feature does not prevent movement of the corresponding barrel halves in a direction perpendicular to a splitting plane (i.e., the plane that divides the barrel into two halves). Consequently, as soil is driven into the sample barrel, the two halves may swell or bow apart from each other. As the adapter coupling and drive shoe constrain the ends of the split barrel, the swelling or separation is greatest at a midpoint between the ends. This may result in the yield strength of the barrel halves being exceeded such that permanent deformation occurs. Deformation of the barrel halves makes it difficult to remove the drive shoe and the adapter coupling.
Therefore, it is an object of the invention to provide a soil sampling system using an improved split barrel design that will constrain the split halves from moving with respect to each other in a direction both lateral to and perpendicular to the splitting plane. It is another object of the invention to provide a split barrel design that will resist permanent deformation of the sampler and have increased useful life by reducing the swelling or bowing apart of the barrel halves from one another as the sampler is driven into the ground. It is a further object of the invention to provide an embodiment of a split barrel sampler that utilizes a tongue and groove feature along the length of the barrel halves to prevent motion parallel to the splitting plane and locking tabs to prevent motion perpendicular to the splitting plane.